Do not switch to a high-cost connection that is not receiving

webrtc/p2p/base/p2ptransportchannel.cc

Index: webrtc/p2p/base/p2ptransportchannel.cc
diff --git a/webrtc/p2p/base/p2ptransportchannel.cc b/webrtc/p2p/base/p2ptransportchannel.cc
index 085185b172fffe7191a4117ff28fe809c29ca7cb..b16667da04bc3c83d666319cd1064193d744ab0c 100644
--- a/webrtc/p2p/base/p2ptransportchannel.cc
+++ b/webrtc/p2p/base/p2ptransportchannel.cc
@@ -183,6 +183,8 @@ void P2PTransportChannel::AddConnection(Connection* connection) {
 //        b) last data received time.
 // iii) Lower cost / higher priority.
 // iv) rtt.
+// To further prevent switching to high-cost networks, does not switch to
+// a high-cost connection if it is not receiving.
 // TODO(honghaiz): Stop the aggressive nomination on the controlling side and
 // implement the ice-renomination option.
 bool P2PTransportChannel::ShouldSwitchSelectedConnection(
@@ -196,6 +198,14 @@ bool P2PTransportChannel::ShouldSwitchSelectedConnection(
     return true;
   }
 
+  // Do not switch to a connection that is not receiving if it has higher cost
+  // because it may be just spuriously better.
+  if (new_connection->ComputeNetworkCost() >
+          selected_connection_->ComputeNetworkCost() &&
+      !new_connection->receiving()) {
+    return false;
+  }
+
   rtc::Optional<int64_t> receiving_unchanged_threshold(
       rtc::TimeMillis() - config_.receiving_switching_delay.value_or(0));
   int cmp = CompareConnections(selected_connection_, new_connection,
@@ -1522,7 +1532,8 @@ bool P2PTransportChannel::IsPingable(const Connection* conn,
   // Always ping active connections regardless whether the channel is completed
   // or not, but backup connections are pinged at a slower rate.
   if (IsBackupConnection(conn)) {
-    return (now >= conn->last_ping_response_received() +
+    return conn->rtt_samples() == 0 ||
+           (now >= conn->last_ping_response_received() +
                        config_.backup_connection_ping_interval);
   }
   // Don't ping inactive non-backup connections.